This invention relates to breakaway couplings for use with a coaxial fuel supply and vapor recovery hose and of the general type disclosed in U.S. Pat. No. 4,763,683 which issued to the assignee of the present invention. Other forms of such coaxial breakaway couplings are disclosed in U.S. Pat. No. 4,827,960 and U.S. Pat. No. 5,135,029. Such coaxial breakaway couplings are commonly used to connect one end of a flexible coaxial hose to a fuel dispensing pump. The opposite end of the hose is connected to a vapor recovery fuel dispensing nozzle, for example, of the type disclosed in U.S. Pat. No. 5,255,723 which also issued to the assignee of the present invention.
In one type of vapor recovery system, such as disclosed in U.S. Pat. No. 5,255,723, the inner conduit of the flexible coaxial hose is used to supply liquid fuel from the dispensing pump to the dispensing nozzle, and the annular passage defined between the inner conduit or tube and the outer conduit or tube is used for returning vapor displaced by fuel in a motor vehicle tank back through the dispensing pump to the underground fuel storage tank. In another type of vapor recovery system the inner conduit or tube within the coaxial hose is used for returning fuel vapor from the dispensing nozzle to the dispensing pump, and the annular outer passage surrounding the inner tube, is used for supplying liquid fuel from the dispensing pump to the dispensing nozzle. This system is commonly referred to as a vapor assist system since the dispensing pump housing encloses a vacuum pump for creating a suction within the inner conduit or tube for sucking fuel vapors through the dispensing nozzle back to the dispensing pump.
When a breakaway coupling is used with a coaxial hose in a vapor assist recovery system, it is desirable for the coupling to incorporate check valves in not only the annular fuel supply passage but also in the center vapor return passage. Thus in the event the sections of the coupling are separated, both the fuel supply passage and the vapor return passage extending from the dispensing pump are closed so that fuel does not exit, and air does not enter the vapor return passage. Such coaxial breakaway couplings for vapor assist recovery systems and which are reconnectable, are produced by Huskey Corporation and Richards Industries, Inc. and sold under the trademarks SAFE-T-BREAK and RICHARDS, respectively.
In some vapor assist recovery systems, the vapor return vacuum pump enclosed within the housing of the dispensing pump creates a substantial suction in the vapor return passage, for example, on the order of 5" Hg, and this suction continues after the sections of the breakaway coupling have separated. Thus with the above coaxial breakaway couplings for the vapor recovery assists systems, it is necessary to use a compression spring which exerts a substantial force for holding the valve within the vapor return passage closed after the breakaway coupling has separated. If the valve does not remain closed, air is sucked past the valve and through the vapor return passage, and the vapor recovery system becomes significantly less effective,